Shift to open-cut Coal Mining and impact on emissions estimate

Open-cut mining now dominates Australian coal production, but its emissions are largely estimated rather than measured, raising concerns about the accuracy of reported reductions.

One of the most important shifts in Australia’s coal mining industry over the last thirty years has been the rapid expansion of open-cut coal mining, which now makes up more than 85% of all coal mine production. 

Underground mining production more than doubled between 1990 and 2015, peaking at 125 million tonnes in 2015 and 2016. Since then, the total volume of underground mining production has contracted to 89 million tonnes. However, its relative share of total coal production has shifted from more than 30% of all coal mined in 1990, to just over 15% of total production, where it has remained relatively steady since 2018. 

Surface or open-cut coal mining has significantly expanded over the past 30 years. In 1990, approximately 190 million tonnes of coal was produced in open-cut mines. By 2003, open-cut mining had doubled its output to 278 million tonnes. A decade later, the growth in open-cut mining had only accelerated, reaching 422 million tonnes in 2013, before peaking at 516 million tonnes in 2019. By the end of 2022, open-cut mining had grown by an incredible 224%.

This rapid expansion has been driven by the expansion of higher efficiency and lower costs of open-cut mining in shallower seams, particularly in central Queensland. Total production has more than tripled over this time, as the relative share of total coal production has risen from just under 70% in 1990, to more than 85% of all coal production nationally by 2022. 

The shift has significant implications for Australia’s estimated fugitive emissions profile. Underground mines, which directly measure their fugitive emissions, have historically been associated with higher emissions due to the nature of their mining process, releasing methane trapped within deeper, higher pressure coal seams. On average, the IPCC estimates that underground mines release 12.5 times more fugitive methane in their mining process than open-cut mines. However, these estimates are largely based on modelled emissions profiles aggregated from global samples, rather than direct emissions monitoring at specific sites.

As a result, the shift towards a greater share of production from surface mining has meant that Australia’s fugitive emissions reporting now rely on estimated emissions levels more than ever. Underground mines currently measure emissions using a well-supported direct measurement approach, though this method is largely applied on a periodic basis. In contrast, open-cut coal mines estimate their fugitive coal mine methane based on gas models originally developed in 1991, rather than direct measurement.

While the rise in open-cut coal mining has decreased the reported emissions intensity of Australia’s coal sector, it has done so largely based on emissions estimates. These emissions estimates have been repeatedly questioned by a diverse array of peer-reviewed satellite comparisons as well as a year-long review of the national emissions reporting system from the Climate Change Authority. As such, the shift in coal production towards open-cut  mining has not only led to a decrease in reported emissions intensity, but it has also led to a parallel increase in the volume and share of fugitive coal emissions that Australia’s coal industry is no longer directly monitoring, but simply estimating. 

While open-cut coal mining production grew by approximately 224% between 1990 and 2022, the growth in reported fugitive emissions has simply not kept up. By 2003, fugitive emissions from open-cut mines had grown by 53%, rather than doubling. Then, by 2013 fugitive emissions had only increased by 74% with negative emissions growth between 2010 and 2013. Then, by the end of 2022, fugitive emissions from surface coal mines had increased by 95%, less than half the rate of growth in production.

This rate of change is even more significant when compared to Australia’s international emissions baseline of 2005. Since that time, open-cut coal production has increased by 45% but fugitive emissions from this same sector have only increased by 13%. As such, since Australia’s emissions baseline was set, surface mining fugitive emissions have grown at less than a third of the growth rate of production.